1. Field of the Invention
The field of art to which this invention pertains is mandrels or core gripping devices, and more particularly, it is directed to a radially expandable mandrel for mounting a core for winding a web of sheet material, such as paper or plastic film.
2. Description of the Related Art
Mandrels, which can be expanded radially to grip a core for winding a web of material, are known to the art.
Various mechanical and pneumatic means have been used to expand this type of mandrel into its core gripping position. A typical example is seen in U.S. Pat. No. 2,890,001 to Triquet which discloses an expanding core shaft for gripping the inside of a paper core. In such patent, the core shaft is assembled into a roll of paper with its expansion element or sleeve radially collapsed between a spaced cone and the conical end of an operating member so that the core shaft slides easily into the core of the roll. After the core shaft is properly located in the end of the roll, an operating shaft is rotated to drive the operating member axially outwardly along an inner tube. The relatively low pitch of the conical surfaces on the expansion sleeve and operating member respectively permit the operating member to slide in expanding relation into the inner end of the expansion sleeve while the relatively high pitch of the cone and its tapered surface resist axial movement of the expansion sleeve. As the inner end of the expansion sleeve expands and grips the inside of the core, further expansion of the inner end of the core sleeve is obstructed and continued outward motion of the operating member causes the expansion sleeve to move axially outwardly in expanding relation over the cone until both ends of the expansion sleeve are formally engaged within the inside of the roll core.
This expandable core shaft provides an effective means for gripping the core during winding. However, the gripping of the core does not occur in a uniform manner; the inner end of the sleeve expands and contacts the inner surface of the core before the outer end makes gripping contact. This uneven force, at the time of contact, could cause axial displacement of the core during mounting. Further, the mechanical means used to expand the shaft in this patent are fairly complex, when compared to the mandrel of the instant invention in which uniform contact of the expanding elements which grip the core is more easily obtained.
The instant invention solves this problem of lack of uniform contact with the core during the gripping operation by providing a mandrel with expandable outer spring-like elements which are cammed outwardly in a uniform manner into gripping contact with the inner surface of the core. These outer elements are restricted axially and their surfaces remain in a substantially horizontal plane during radial movement and during contact with the core. This controlled contact prevents axial displacement of the core which might be caused by uneven contact.
U.S. Pat. No. 4,492,346 shows an example of an expandable shaft in which camming action is used to move a plurality of core engagers into engagement with a core. A positive force is also provided to retract the core-engagers which may have become embedded in the surrounding core. Each of the engagers is an integral metal unit that includes a number of spaced core engaging lugs on its outer surface.
As compared to the teachings of this patent, the camming movement, of the outer elements, in the mandrel of this invention, is accomplished in a relatively uncomplex manner by moving spaced apart inner elements of the mandrel inwardly, toward each other, under the outer elements. These elements have matching tapered surfaces which provide the camming action. Again since only the inner elements are moved axially and since such elements never contact the core, core displacement caused by axial movement, due to contact during mounting, is prevented.
A unique means is also provided to simultaneously move the inner elements axially inwardly to thereby radially move the outer elements into uniform gripping contact with the core. This means is in the form of a floating acme screw, which will further be described in detail. Such screw additionally assures that uniform equal gripping forces are placed against the core surface by each of the outer elements, irrespective of diameter variations in the core. This feature plays a significant role in providing improved runout of the core surface.
By providing these and other advantages, the expandable mandrel of this invention gives to the art an improved means of mounting cores for winding, and in so doing provides improved properties in the wound roll.